During the existing oil extraction process, it is necessary to seek for “an artificial method” if crude oil can not naturally flow out from the production well for lack of internal pressure or other reasons, and at present the beam pumping unit is most common, which is normally called as a “Nodding machine”. The beam pumping unit is mainly comprised of a beam-linkage-crank mechanism, a reduction gearbox, a three-phase asynchronous motor, auxiliary devices and the like. When extracting oil, it has the low overall efficiency, small power factor and high electrical energy consumption. Further, the beam pumping unit has the huge size, low energy saving efficiency, high cost and low yield, and it is inconvenient to execute the installation and maintenance.
Therefor, the Chinese patent CN202181885U discloses a hydraulic pumping unit, which comprises a secondary control hydraulic unit, an oil cylinder controlled by the secondary control hydraulic unit to drive reciprocating movement of a pumping rod, a sensor for setting a stroke of the piston rod (i.e., the pumping rod) of the oil cylinder, a asynchronous motor in transmission connection with the secondary control hydraulic unit, a potential energy accumulator (preferably in the form of a flywheel) in transmission connection with the asynchronous motor, and a secondary control hydraulic unit controller adapted to control the forward and reverse motion of the secondary control hydraulic unit based on the signal from the sensor. By means of such type of hydraulic pumping unit, the stroke and speed can be flexibly controlled according to the characteristics of the oil well, thereby achieving the sufficient oil extraction and enhancing the yield. Further, the electrical energy consumption is reduced, with the improved production efficiency, since the potential energy accumulator can accumulate the potential energy and thereafter release it.
In the hydraulic pumping unit, the flywheel, the asynchronous motor and the secondary control hydraulic unit share one shaft. During the downward movement of the pumping rod, the secondary control hydraulic unit as a motor drives rotation of the flywheel to convert the gravity potential energy of the pumping rod and so on into rotational kinetic energy. Thus, the energy conversion efficiency mainly depends on the variation range of the rotation speed of the flywheel. According to this design, the flywheel is mechanically coupled to the motor, that is, the flywheel and the rotor of the motor must experience the synchronous rotation. Thus, the speed variation range of the flywheel, which is critical to the energy recycling utilization, is directly constrained by the velocity range of the motor. Just for this reason, it is desired to allow for the maximum velocity variation range for the motor. Since the synchronous motor has a strictly fixed speed, the asynchronous motor is the option as described above. However, even for the asynchronous motor, the allowed speed variation range is still limited. The energy recycling utilization is therefore greatly restricted.
On the other hand, if the speed variation range is fixed, the energy recycling capacity is only related with the inertia of the flywheel. This will lead to the very great size and weight of the flywheel, thereby causing huge problems for the actual production and installation.
In this case, it is urgent to provide a reliable hydraulic pumping unit which has the simple structure and the high energy recycling utilization efficiency.